That computer is so slow, it really doesn't matter what video card you plug into it.
It's like asking what are the best "Z rated" high-speed radial tires to put on a stock 1964 Volkswagen.
Any decent PCI video card will do. Don't go out and buy an expensive one, your machine will never
fulfill the cards' capabilities. Look for something in the $30 price range.
Don't buy an AGP card either, you don't have the socket to plug it into.